Electronic devices, including energy sensitive solar cells, are vulnerable to various types of degradation. The present invention is concerned with the stabilization of interfaces and intraconnections in devices, and more particularly to the stabilization of devices such as solar cells and integrated circuits.
One important kind of degradation arises from thermal soaking or cycling. In integrated circuits, thermal soaking destabilizes, for example, the aluminum/silicon interface because of inter-diffusion. Solar panels that convert light to electricity degrade in performance because of deterioration , for example in the case of amorphous silicon cells, of the electrical contact between a front electrode, usually conductive tin oxide, and a back electrode, usually aluminum. It is recalled that a common panel configuration of intraconnected amorphous silicon solar cells is glass/tin oxide/ p- a-Si:C:H/i- a-Si:H/n- a-Si:H/Al. Another degradation mode to be noted here is the interdiffusion of silicon and aluminum at the back contact interface.
The illustrative modes of degradation enumerated above are continuous and non-reversible, under thermal cycling. They seriously curtail the useful lifetime of the devices.
Amorphous silicon solar panels are manufactured, generally, by successive deposition of various layers on a suitable substrate. For example, transparent conductive tin oxide deposited on glass is a common substrate. Individual cells using this tin oxide as the front electrode are created by laser patterning the tin oxide. This is followed by the deposition of p-, i- and n- type of amorphous silicon based alloys. The semiconductor layers thus deposited on tin oxide are suitably scribed to expose thin lines of the underlying oxide(the front electrode) of demarcated cells. The final step is the deposition of the back electrode, for example aluminum, through an appropriate procedure to produce an intraconnected solar panel.
When amorphous silicon is opened up as described above to expose the underlying tin oxide front electrode, it is likely that the site thus created will not provide a good and stable contact on subsequent metallization and subjection to thermal cycling or soaking. Further, under the same conditions of thermal soaking, there is a gradual deterioration of the interface between silicon and the electrode like aluminum because of interdiffusion as indicated by accelerated testing and subsequent analysis.
Accordingly, it is an object of this invention to improve the quality of the intraconnections in devices, particularly the intraconnections in solar cells.
Another object of the invention is to reduce the degradation of the intraconnections that occurs during their thermal cycling, particularly in solar cells.
Still another object of the invention is to reduce the interdiffusion at interfaces, particularly in solar cells and integrated circuits, between a semiconductor and a metal contact.